Resin bonding is a well-known treatment procedure for tooth restoration in modern dentistry. It entails the application of an acrylic resin material to the tooth which is hardened by either a chemical reaction with another element or cured by ultraviolet or visible light wavelength radiation. Bonding is achieved by a micro-mechanical interlocking of the hardened resin into irregularities in the surface of the tooth. In order to facilitate this bond, the enamel of the tooth is first "etched" with an acid solution. During etching, the enamel surface becomes roughened and enamel prism patterns are created containing "tags" which provide the greatest amount of enamel surface area and mechanical interlocking between the tooth and the resin-bonding material. Etchants containing phosphoric acid have been shown to provide the best enamel surface characteristics for micro-mechanical interlocking of the resin.
Dentists currently use two forms of phosphoric acid etchant, a liquid or a gel composition. The liquid phosphoric acid has the advantage of great surface wetability and is easily rinsed away, but has the disadvantage of uncontrolled flow over the surface of tooth. The gel composition has the advantages of holding its position on the tooth and being visible because of a color dye in the gel, but the gel can often leave organic debris residue if not rinsed totally from the tooth surface. For this reason, a heavy water spray rinsing of 20-40 seconds for each etching procedure is recommended for gel-type etching. With either the liquid or the gel etching procedure, a preliminary step of cleansing of the tooth enamel surface with pumice is recommended.